A major policy issue today is when the next change in the trend of period fertility will occur. Recently, fertility fluctuations have produced large and long-lasting effects on the economy and important societal institutions. The primary objective of the research proposed here is to examine the Easterlin fertility hypothesis, which holds that changes in the relative economic prospects of young people contribute to changes in fertility, where relative economic prospects are operationally defined as the ratio of offsprings' current income to their parents' income during the offsprings' adolescence. The principal weakness of previous research on the Easterlin hypothesis is the questionable validity of relative economic status measures, which perhaps explains the conflicting evidence obtained from studies relying on aggregate and individual cross-section data. With the Social Security Administration's cooperation, longitudinal data from the Wisconsin Study of Social and Psychological Factors in Socioeconomic Achievement will be used to reexamine the Easterlin hypothesis. The proposed data base is uniquely suited to this task, since it will include, for men, complete fertility and marriage histories, a stream of Social Security earnings records for the first fourteen years after high school, and the income of the individual's parents when he was an adolescent. Two major analyses will be performed. The first will test a previously unexamined hypothesis, that relative income influences age at marriage, thereby affecting the pace of family-building. The second will study marital fertility, using a subsample of married men. To gain full advantage of the longitudinal data, fertility during successive intervals will be analyzed sequentially. To the extent the data permit, this second analysis will be extended by examining another fertility hypothesis (relating to social mobility), and by explicitly considering possible connections among relative incomes, women's work, and marital fertility.